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Interceptor vs. Heartgard

A concern of mine, need some feed back to this…I was playing on the web a couple of days ago and came across this warning, ‘COLLIES AND SHELTIES MUST BE ON HEARTWORM PREVENTITION PLAN, AND MUST BE PLACED ON INTERCEPTOR. (HEARTGARD HAS PROVEN TOXIC AND EVEN FATAL TO THEESE BREEDS.)’
My concern is Heartgard vs. Interceptor. Our vet must not know about this, for he has us using Heartgard. Since coming across this warning I have been trying to find out if this is true, and if so, where I can find the documentation showing that it is true. I want to give it to my vet, so he is up to speed on this matter. Please help.
Do I change to Interceptor to be on the safe side? I talked to my vet this morning — he said he would give me a prescription for Interceptor if I wanted to change.

13 comments to Interceptor vs. Heartgard

Patti, let me first help you relax a bit. If your Shelties have been taking Heartgard with no ill effects so far, then you probably don’t have to worry. But…

The problem of the medicine in Heartgard being potentially fatal to Collies, Shelties, Border Collies, possibly Bearded Collies, Australian Shepherds, and a few other breeds (mostly herding breeds, although I’ve heard reports that other breeds, including Whippets and some other sighthounds may also be affected) is well documented. Unfortunately, the makers of Heartgard refuse to acknowledge the now-proven potential for problems, and the result is that many vets have never heard about it.

The problem is in a gene, called the MDR1 (Multi-Drug Resistance) gene, that has multiple variants. About 15% of individuals of Shelties (different percentages, ranging from less than 5% to over 70%, apply to the other breeds I mentioned above) have a variant of this gene that makes them highly sensitive to a number of medications, of which ivermectin (the medicine in Heartgard) is only one. Of course, different individuals will have different levels of sensitivity and will respond differently to these medications. The “sensitivity” can range from difficulty metabolizing the drug (meaning that it stays in the system much longer than normal, consequently having a more pronounced effect) to greatly increased action of the drug (meaning that its effects are much stronger than the dosage would normally cause).

Sensitive dogs lack a protein (P-Glycoprotein), which is responsible for pumping out many drugs and toxins from the brain, and such dogs show signs of toxicity because they are unable to stop drugs from permeating their brains. The results range from neurological damage to death.

I have personally had a tragic experience with ivermectin. Having heard rumors about such problems back in 1992, I asked my vet about it and was assured that there was nothing more than a very few unconfirmed reports of allergic reactions to the drug. So, I gave a single dose to my Sheltie, Ellie. Within 72 hours, she was literally at death’s door. Intense intervention by a vet saved her life, but she was “sickly” for the remaining 11 months of her life, and she never fully recovered. She died of liver and kidney failure that I am convinced was closely related to the ivermectin.

You can have your dogs tested for the MDR1 variant (it’s a 144-base pair version of the gene, compared to the normal, “in the wild” 148-base pair version that is carried by dogs who do not have the ivermectin sensitivity). The cost seems to run about $60, IIRC, and USA residents can have it done by:

(I did see a note that suggested that the $60 pays for a kit that allows four tests, not only one. I haven’t confirmed this independently, though.)

Other drugs that are known to cause similar reactions in sensitive dogs include: Acepromazin, a pre-operative and anti-anxiety medication; butorphanol, used for pain; doxorubicin, vinblastine, vincristine and cyclosporin, used for chemotherapy; loperamide (Imodium), used for diarrhea; and digoxin, a heart medication.

I especially worry about loperamide, because it’s darned near indispensable when one had dogs with digestive upsets! So far, we’ve not had any problems when we give loperamide to dogs with diarrhea, but maybe we’ve just been lucky; I think (but nobody has confirmed to me) that the loperamide sensitivity associated with the MDR1 variant isn’t as delicate as the ivermectin sensitivity.

NOTE: According to the Washington State University study, Collies and long-haired whippets are the most affected (65-70%), while border collies are affected about as much as the average mixed-breed dog (5%). In spite of that report, I would never take the chance of giving ivermectin to a border collie!

This is SO SERIOUS, that Sheltie Rescue of Utah’s adoption contract includes a special clause, which MUST be initialed by every adopter, that absolutely prohibits the use of ivermectin on any Sheltie we place. Violation of that provision is so serious that we WILL recover any Sheltie we’ve placed if we discover that the adopter has been giving ivermectin. (We haven’t added the other problematic drugs to the contract, but we’re considering it.)

Tell your vet that you are unwilling to take the risk, whether it’s a large risk or a small one. The potential cost is far too high. Why take the chance with your dog’s life, when it costs no more to give heartworm preventative containing milbemycin, the drug in Interceptor?

Thank you Sheltie Jim for all the detailed information you have given us. DeBoys will be taking Interceptor from now on!!! I would rather be safe than sorry…they are my babies.

For your dogs with upset digestive to diarrhea — Try just giving them a couple of table spoons of PUMPKIN…this has helped my boys. When Brutus was recovering from his surgery, he ended up having diarrhea so bad that it was more of a liquid, gave him his PUMPKIN instantly cleared him. I AM A BELIEVER — TRY IT.

Sherry, most people I to whom I talk who use pumpkin in their dogs’ diets use canned, or at least cooked, pumpkin. I think that raw pumpkin might have the opposite effect, but maybe I’m just uneducated about it.

Ivermectin is a drug that causes problems in herding dog breeds with the MDR1 gene mutation. But the microgram dose that is in Heartguard has been used safely even in known mutant dogs. When it causes problems is when the dog is treated with Ivermectin for parasites (mange) or when they get into it at another source (such as eating horse dewormer at a barn).

Personally, we would never choose to use a chemical-based product on our dogs, and several of our own customers have had dogs die because of the chemical dewormers their vet gave them (and this includes those based on Ivermectin).
There are natural, herbal products that are just as effective, and completely safe (for all breeds). Check out a company called Natural Wonder Pets – we use their products all the time with our own dogs.

Mark, I’ve read a lot of research in this area, and your comment is the first I’ve ever heard of “natural, herbal products” being effective as a heartworm preventative and/or treatment. Needless to say, I’ll check out Natural Wonder Pets and see what they have; I’ll also do additional research to see if their approach is acknowledged (favorably or otherwise) by the leading researchers in this area. Thanks for the pointer.

But your comment said “(and this includes those based on Ivermectin)” — that is exactly the problem that my first response to Patti and De Boys identified — dogs dying from Ivermectin. If you meant “…based on milbemycin…”, then I want to say that the only reports I’ve read of dogs killed by milbemycin were either (a) severely overdosed or (b)already infected with heartworm and died because the worms killed by the milbemycin decomposed inside the dogs’ hearts.

SheltieJim, I’m doing some research on HeartGard for my border collie/lab mix. We’ve had him 7 months. Each time we’ve given him his HeartGard pill, the next day he became very sick – throwing up terribly. The last time he took it at night, this was the third time – we broke it up in his food. The next morning he was eating a bunch of grass and finally threw up. I was very scared as he hacked so much he just fell over – I think he passed out for about 1 second. Now I’m seeing that this pill could be the cause. I will call our vet to get alternative info from them but wanted to get you input too. We also need to start him on Frontline or some kind of flee and tick prevention but at this point we’re scared to do that also. Please let me know your thoughts for our 8 month old Lab/border collie mix; “Ace”. thank you

Jon, congratulations on adopting a wonderful lab/BC mix. I’ll be he’s as cute as all get-out!

Border Collies are among the breeds of dog that can have the MDR-1 mutation, which means that BC mixes can also carry it.

Of course, there’s no way that I can be certain that Ace has the mutation and is thus sensitive to Ivermectin. But the behaviors you describe are common among MDR-1 dogs when given Ivermectin. But I should clarify one thing: Just because a dog has the MDR-1 mutation doesn’t mean that he/she will necessarily have any one kind of reaction or that the reaction will be death. Different dogs, even from the same litter, can often have varying degrees of sensitivity to the various drugs to which MDR-1 dogs are known to be sensitive.

The very best thing you can do is to have your dog tested for the MDR-1 mutation. It’s very easy, but not dirt cheap; it costs (I think) either $60 or $70/dog. Contact:
Washington State University
Veterinary Clinical Pharmacology Laboratory
P.O. Box 609
Pullman, WA 99163-0609
Phone: 509-335-3745 Fax: 509-335-6309
Website: http://www.vetmed.wsu.edu/depts-VCPL/test.aspx
Email: VCPL@vetmed.wsu.edu
and they’ll send you a kit; you do a cheek swab (inside the mouth) on your dog with a device in the kit and just mail it back. Within a few weeks, you’ll get a report back.

If your dog is NOT MDR-1, then the Ivermectin in HeartGard is *probably* not the cause of Ace’s reactions. I say “probably” because he might have a specific allergy to something (Ivermectin or filler ingredients) in HeartGard.

Unhappily, Novartis, the company who manufactured Interceptor, the medication containing milbemycin, has quit making Interceptor, which has a very large number of people (vets and dog owners) outraged. They do, however, make a product called Sentinel, which contains milbemycin for heartworm plus another ingredient (Lufenuron) used to deal with fleas as well. We don’t have fleas where we live, so we don’t want the “added ingredient” — we hate giving our dogs medicines for problems that they do not and will not have. But you apparently do have a flea problem, so Sentinel might be appropriate for you.

If you can’t afford the MDR-1 test (or would prefer just to change medications simply because there’s the possibility that Ace has the MDR-1 mutation), you should try Sentinel and see if he reacts poorly to that. If not, then just stop using HeartGard and use Sentinel instead. (NOTE: A lot of vets are beginning to report that Ivermectin is beginning to lose effectiveness against heartworms in various parts of the country.)

Please reply here when you have learned more so we know that Ace is doing OK!

I wanted to update you on Ace and ask another question. Ace is doing well. About 80 lbs. now. We still have not given him any kind of Heartworm meds based on how sick it made him. We just gave him his first dose of Advantix about 2 weeks ago. Seems that it may have caused him some constipation and then very loose poops. He was getting us up 2 times in the middle of the night to go and had an accident in the house when we were gone – not his fault. He seems to have turned the corner the last 2 nights as he has not had to go and his poops are looking formed again. Now, my question; we talked to our vet and she conferred with her partner vet and agreed that Advantix was good to use with Sentinel and suggested we give Sentinel about 2-3 days after Advantix. Problem; I can’t find Sentinel around here. We are going out of town for a day and are going to try our vets boarding for 2 nights for Ace and they require him to be on Heart meds. What are your thoughts on Revolution? Is it comparable to Sentinel based on the mutation, chemicals, etc that we have talked about and concluded Sentinel was a good choice? I really want to try Sentinel but I can’t find it and may have to order it online except it might not get here in time for him to be boarded. I certainly appreciate your input on all of this. Let me know your feelings. Thanks again.

Jon, please accept my apologies for failing to respond to your post for over two months. I have been largely out of the country on day-job business during that time, and frantically trying to catch up when I was back at home.

I have not personally used Advantix, so I’m reluctant to give any advice about it. I can tell you that a number of people in the Sheltie rescue community have tried it and had results ranging from success to disastrous. Many Shelties have gotten very sick when given Advantix, according to my colleagues. However, I am reluctant to take anecdotal evidence, even from people I generally trust, to extrapolate that to condemnation of the medicine. I have not done due diligence and researched the various veterinary medical sites for further information, but I suggest that you might want to do so yourself. (And, of course, Advantix is effective only against external parasites, and not heartworm.)

I have also not personally used Revolution, but my research indicates that it is successful at preventing heartworm infection, but not at controlling even microfilaria after infection; by contrast, heartworm medications that are administered internally (e.g., by mouth or by injection) do control microfilaria. Of course, Revolution will not be effective on a dog with adult heartworm infection, and other medications will probably kill the heartworms in situ where they will decompose and probably kill the dog. My problem with Revolution is that its active component is selamectin, which is a close chemical cousin to ivermectin, to which Shelties, Collies, and several other breeds have sensitivities up to and including death. (Incidentally, I have the same problem with Advantage, which is based on another cousin to ivermectin, moxidectin.)

If I were in your shoes, I would definitely try to find Sentinel online and purchase it there. You might need a prescription from your vet, so be prepared to have to request one. I’m still very unhappy that ordinary milbemycin (Interceptor) is no longer available, because the lufenuron in Sentinel is not needed in my area.